1. Technical Field
The present invention relates to skis utilized in winter sports, and adapted to slide on snow and ice.
2. Background Art
A ski generally comprises a lower sliding surface having an angle iron on each lateral side edge for engaging snow, two lateral side surfaces defining the width of the ski, and an upper surface having means, located in a central binding zone, by which a user attaches his foot to the ski. The leading end of a ski is usually curved upwardly in the form of a spatula; and the ski is relatively narrow in width compared to its length which defines a longitudinal direction.
In conventional skis, the thickness of the body of a ski varies along the length of the ski in the longitudinal direction having a maximum in the binding zone where the flexional movements are a maximum during use of the ski. Because the thickness of the ski near the central zone is a maximum, and the thickness near the front and rear ends is a minimum, a uniform load distribution is achieved as disclosed in French Patent No. 985,174, for example.
French Patent Application Nos. 86 07849, 86 07850, 86 07851, and 86 07852, disclose skis whose lateral surfaces or edges have inclinations that vary along the length of the ski. The contact of these edges with the snow increases the stability of the skier particularly during execution of turns.
Conventional skis generally have a composite structure in which different materials are combined in the manner such that each composite operates in optimal fashion taking into account the distribution of the mechanical stresses in the skis. The composite structure comprises mechanical resistance or reinforcing elements or mechanical resistance layers made of material having a high mechanical resistance to strain and substantial rigidity so as to resist flexional and torsional stresses produced in a ski during its use. The conventional structure further includes filler elements and absorption elements.
The two principle modern composite structures finding current wide scale application in skis are the so-called sandwich and casing structures. In a typical sandwich structure, such as described in FIGS. 1 and 2 of French Patent No. 1 124 600, and in French Patent No. 2 069 824, the ski comprises a central core made of cellular material, which may be partially hollow, reinforced above and below respectively by an upper resistance layer and a lower resistance layer, the resistance layers having mechanical resistance and rigidifying qualities greater than those of the core itself.
It has been observed that a sandwich structure provides a ski that has the best sliding characteristics in a straight line, i.e., when the ski is moving in the longitudinal direction of the ski. On the other hand, the lateral gripping quality of such skis on inclines, or in turns, is not optimal; and for this reason, skis having a casing structure are preferred to optimize skiing on inclines or in executing turns.
In a typical casing structure, such as described in French Patent No. 985,174, and in FIG. 3 of French Patent No. 1,124,600, the ski comprises an internal core made of cellular material which may be partially hollow, and mechanical resistance elements surrounding the core in the form of layers that constitute a casing for the core. The casing structure confers superior elasticity and mechanical resistance properties to the ski in flexion, and a high torsional resistance along the longitudinal axis of the ski.
Skis having a casing structure have optimal lateral gripping qualities (en devers) for skiing on inclines or executing turns. On the other hand, the straight-line sliding characteristics of such skis are less desirable than skis having a sandwich structure.
As in the case with the exterior shape of a ski, the casing has a thickness which varies longitudinally by following the exterior shape of the ski. Despite this variable thickness, which leads to a casing having a greater thickness and rigidity at the center of the ski and less near the ends, the intrinsic properties of the casing produce sliding characteristics which are less desirable than those associated with a sandwich structure.
As a result, it is customary to select skis on the basis of the use to which the ski will be put. For example, a ski having a sandwich structure is selected for down hill competition because this structure has superior sliding characteristics; and a ski having a casing structure is selected for slalom competition because a casing structure has superior ice-gripping qualities.